The present disclosure relates to power supply apparatuses that control an output voltage based on a difference between a predetermined reference voltage and a feedback voltage obtained from the output voltage, and image forming apparatuses including the power supply apparatuses.
Image forming apparatuses, such as copy machines, printers, and facsimile apparatuses, operate in one of a normal operation mode and a power saving mode (also referred to as a sleep mode). The normal operation mode represents an operation mode in which the image forming apparatus is on standby so as to operate immediately when a print instruction is inputted. The power saving mode represents an operation mode in which the image forming apparatus is on standby so as to reduce power consumption of the apparatus by supplying power to a part of components. For example, in a case where a standby time period from power-on to input of a print instruction is shorter than or equal to a predetermined time period, the image forming apparatus operates in the normal operation mode in which power is supplied to all of load devices. On the other hand, in a case where the standby time period is longer than the predetermined time period, the image forming apparatus is controlled so as to shift from the normal operation mode to the power saving mode after elapse of the predetermined time period, and supply power to a part of the load devices.
When the image forming apparatus is caused to shift from the power saving mode to the normal operation mode, increase of loads causes abrupt increase of load current, to reduce voltage, whereby operations of the load devices may become unstable. For example, when an output voltage from a power supply device of the image forming apparatus becomes lower than a rated voltage of a load device due to the reduction in voltage, the load device may not operate. On the other hand, when the image forming apparatus is caused to shift from the normal operation mode to the power saving mode, reduction of the loads causes abrupt reduction of load current, whereby voltage may be excessively increased. Also in this case, operations of the load devices may become unstable. Therefore, to date, feedback control has been performed in which, for power supply devices of image forming apparatuses, feedback of an output voltage outputted to a power supply path for a load device is performed, and power supply is controlled so as to reduce a difference between the voltage (feedback voltage) and a predetermined reference voltage.
In order to realize further reduction of power consumption, the image forming apparatus may be designed such that, when the image forming apparatus shifts to the power saving mode as described above, driving voltage for a calculation device such as a CPU used in the image forming apparatus is reduced. However, if a power supply device is structured to perform control for reducing the driving voltage of the calculation device, in addition to the feedback control, a power supply circuit of the power supply device is complicated. Further, a commercially available DC/DC converter is an IC in which a rectifier circuit, a switching circuit, and a feedback control circuit are integrated with each other, and therefore it is difficult to incorporate, in the DC/DC converter, a circuit for reducing driving voltage of the calculation device.